Creep mechanism of gas-pressure-sintered silicon nitride polycrystals I. Macroscopic and microscopic experimental study

Abstract

The creep behaviour and microstructure of two silicon nitride ceramics have been investigated. Compressive creep tests were performed at temperatures between 1450 and 1700°C at stresses between 6 and 90 MPa in an Ar atmosphere. The creep behaviour was characterized by a stress exponent lower than one for both materials, with an average value n ≈ 0.6 over the whole range of stresses and temperatures, and with apparent activation energies between 470 and 530 kJ mol⁻¹. The study of the microstructural evolution revealed the absence of dynamic grain growth and, in some cases, evidence of grain rearrangement. Partial coalescence of cavities was observed only at the highest stress, but this did not result in accelerated creep.

Acknowledgements

This work was supported by the Brite–Euram Project BE97-4544 during the stay of J.J.M.-M at the University of Seville. The authors wish to thank Dr M^a Isabel Osendi (Instituto de Cerámica y Vidrio, Arganda del Rey, Madrid, Spain) and Mr Thomas Hirschmann (CFI, Rödental, Germany) for performing plasma etching on undeformed and crept samples. One of the authors (J.J.M.-M) wishes to thank Dr Naoki Kondo (Synergy Materials Center, Agency of Industrial Science and Technology, Nagoya, Japan) for his comments and for providing copies of his papers.

Notes

 Present address: Departamento de Física, Universidad de Extremadura, Avenida de Elvas, s/n 06071 Badajoz, Spain

Additional information

Notes on contributors

A. Domínguez-Rodríguez ‡

 Present address: Departamento de Física, Universidad de Extremadura, Avenida de Elvas, s/n 06071 Badajoz, Spain